1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a color filter layer on an array substrate and a manufacturing method thereof.
2. Discussion of the Related Art
A liquid crystal display (LCD) device is driven based on the optical anisotropy and polarization characteristics of a liquid crystal material. In general, the LCD device includes two substrates that are spaced apart and face each other, and a liquid crystal material layer interposed between the two substrates. Each of the substrates includes electrodes that face each other, wherein a voltage applied to each electrode induces an electric field perpendicular to the substrates between the electrodes. An alignment of liquid crystal molecules of the liquid crystal material layer changes by varying an intensity or direction of the applied electric field. Accordingly, the LCD device displays an image by varying light transmittance through the liquid crystal material layer in accordance with the arrangement of the liquid crystal molecules.
FIG. 1 is an expanded perspective view illustrating a related art LCD device. As shown in FIG. 1, the LCD device 11 includes an upper substrate 5, referred to as a color filter substrate, and a lower substrate 22, referred to as an array substrate, having a liquid crystal material layer 14 interposed therebetween. On the upper substrate 5, a black matrix 6, and a color filter layer 8 are formed in a shape of an array matrix including a plurality of red (R), green (G), and blue (B) color filters surrounded by corresponding portions of the black matrix 6. Additionally, a common electrode 18 is formed on the upper substrate 5 to cover the color filter layer 8 and the black matrix 6.
On the lower substrate 22, a plurality of thin film transistors (TFTs) T are formed as an array matrix corresponding to the color filter layer 8. A plurality of crossing gate lines 13 perpendicularly cross a plurality of data lines 15. The TFTs T are positioned such that each TFT T is located adjacent to an intersection of one of the gate lines 13 and one of the data lines 15. Furthermore, a plurality of pixel electrodes 17 are formed on a pixel region P defined between the gate lines 13 and the data lines 15 of the lower substrate 22. The pixel electrode 17 includes a transparent conductive material having high transmittance, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).
As further shown in FIG. 1, a storage capacitor CST is disposed in each pixel P and connected in parallel to the pixel electrode 17 of the pixel. The storage capacitor CST is comprised of a portion of the gate line 13 as a first capacitor electrode and a metal layer 30 as a second capacitor electrode. Since the metal layer 30 is connected to the pixel electrode 17 through a contact hole, the storage capacitor CST is electrically contacted to the pixel electrode 17. The metal layer 30 may be made of the same material as the data line 15. When fabricating the LCD device 11 of FIG. 1, the upper substrate 5 is aligned with and attached to the lower substrate 22. In this process, the upper substrate 5 may be misaligned with the lower substrate 22 and light leakage may occur in the completed LCD device 11 due to an error margin in attaching the upper and lower substrate 5 and 22.
FIG. 2 is a cross-sectional view along the line II-II′ of FIG. 1, illustrating a pixel of the related art liquid crystal display (LCD) device. As shown in FIG. 2, the related art LCD device includes the upper substrate 5, the lower substrate 22, and the liquid crystal layer 14. The upper and lower substrates 5 and 22 are spaced apart from each other, and the liquid crystal layer 14 is interposed therebetween. The upper and lower substrates 5 and 22 are often referred to as an array substrate and a color filter substrate, respectively, because the color filter layer 8 is formed upon the upper substrate and a plurality of array elements are formed on the lower substrate 22. As further shown in FIG. 2, the thin film transistor T is formed on an inner surface of the lower substrate 22, and a passivation layer 40 is formed on the thin film transistor T. The thin film transistor T includes a gate electrode 32, an active layer 34, a source electrode 36, and a drain electrode 38.
Referring to FIG. 1, the gate electrode 32 extends from the gate line 13 and the source electrode 36 extends from the data line 15. The gate, source, and drain electrodes 32, 36, and 38 are formed of a metallic material while the active layer 34 is formed of silicon. The pixel electrode 17 that is formed of a transparent conducting material is disposed in the pixel region P.
As shown in FIG. 2, the pixel electrode 17 contacts the drain electrode 38 and the metal layer 30. As mentioned above, the gate electrode 13 acts as a first electrode of the storage capacitor CST and the metal layer 30 acts as a second electrode of the storage capacitor CST. Thus, the gate electrode 13 and the metal layer 30 are parts of the storage capacitor CST.
Still referring to FIG. 2, the upper substrate 5 is spaced apart from the first substrate 22 over the thin film transistor T. On the rear surface of the upper substrate 5, a black matrix 6 is disposed in the position corresponding to the thin film transistor T and the gate line 13. The black matrix 6 is formed on the entire surface of the upper substrate 5 and has openings corresponding to the pixel electrode 17 of the lower substrate 11, as shown in FIG. 1. The black matrix 6 prevents light leakage in the LCD panel except for the portion for the pixel electrode 17. The black matrix 6 protects the thin film transistor T from the light such that the black matrix 6 prevents generating of photo current in the thin film transistor T. The color filter layer 8 is formed on the rear surface of the upper substrate 5 to cover the black matrix 6. Each of the color filters 8 has one of the red, green, and blue colors and corresponds to one pixel region where the pixel electrode 17 is located. A common electrode 18 formed of a transparent conductive material is disposed on the color filter layer 8 over the upper substrate 5.
In the related art LCD panel mentioned above, each pixel electrode 17 corresponds to each color filter. Furthermore, in order to prevent a cross-talk between the pixel electrode 17 and the gate and data lines 13 and 15, the pixel electrode 17 is spaced apart from the data line 15 by the distance A and from the gate line 13 by the distance C, as shown in FIG. 2. The open spaces A and C between the pixel electrode 17 and the data and gate lines 15 and 13 cause a malfunction, such as light leakage, in the LCD device. Typically, the light leakage mainly occurs in the open spaces A and C. However, the black matrix 6 formed on the upper substrate 5 should cover those open spaces A and C. But when arranging the upper substrate 5 with the lower substrate 22 or vice versa, a misalignment may occur between the upper substrate 5 and the lower substrate 22. Therefore, the black matrix 6 is extended to more than cover those open spaces A and C. That is, the black matrix 6 is designed to provide an aligning margin to prevent light leakage. However, when extending the black matrix, an aperture ratio of the liquid crystal panel is reduced in as much as the aligning margin of the black matrix 6 is increased. Moreover, if there are errors in the aligning margin of the black matrix 6, the light leakage occurs in the open spaces A and C, and deteriorates the image quality of the LCD device.